Ingenious Prodigy

The trick this card pulls is turning stored size into a metered card-draw engine, and the two abilities are in productive conflict. The counters it enters with make it a real body, but every upkeep asks you to trade a point of that body for a card, so the creature slowly hollows itself out to keep the cards flowing. That tension makes the X flexible in a way flat X-drops rarely are: cast it small and it is a cheap chump that dies before it draws much, cast it large and it is both a clock and a multi-turn draw spell you can shut off the instant you would rather keep the stats. Skulk is the mechanic that lets the invested mana actually connect. Because it cannot be blocked by anything with greater power, a Prodigy loaded with counters slips past the wall of bigger blockers a controlling opponent parks in front of it, and the drain of upkeep counters gradually shrinks its power back toward evasive range if it started as the biggest thing on the board. The result is a self-regulating value creature: it wants to be big enough to hit and small enough to sneak through, and it converts the gap between those two states into cards. Whether you prioritize the beatdown or the draw is a choice you get to remake every upkeep.